HAYWARD -- Police are investigating the death of an unidentified man whose body was found along Interstate 880 early Wednesday.

The man apparently fell from an overpass and was struck by a big-rig truck in the southbound I-880 lanes near the Industrial Parkway on-ramp, just before 4:45 a.m., California Highway Patrol Sgt. Leonard Tombac said.

Officers responded to the scene and pronounced the man dead. The man, possibly in his late 20s, has not yet been identified, Tombac said.

The incident shut down two southbound lanes of I-880 and the Industrial Parkway on-ramp for several hours so officers, assisted by the Hayward Police Department, could investigate.

It was not immediately known what caused the man to fall.

Hayward police Sgt. Mark Ormsby said that police were interviewing witnesses late Wednesday and that the fatality remained under investigation.

The driver of the big rig was not cited, Tombac said.

Anyone with information about the case is asked to call Hayward police at 510-293-7000 or the anonymous tip line: 510-293-7197.